Pigments are important for various cosmetic applications, such as those for the face, eye, lip and nail. For instance, when used as part of facial foundations, pigments help to cover facial blemishes or blend uneven colors on the face. When used as part of facial powders, pigments provide coverage of complexion that is considered by the user as undesirable. When used as facial blushes, pigments enhance the cheeks with colors that are trendy or desirable.
The dispersion of pigments is an important aspect of personal care formulations. Pigments are typically delivered in one of two common types of emulsions: water-in-oil (W/O) emulsions or oil-in-water (O/W) emulsions in the presence of emulsifiers. The nature of the emulsifier is an important factor as to what type of emulsion that may be formed, and thus how the dispersion of the pigments will occur.
Regarding the type of emulsion to be formed, the Bancroft rule state that an emulsifier will promote dispersion of the phase in which it does not dissolve. Accordingly, when a pigment is combined with a lipophilic emulsifier (that is, hydrophobic), water is the dispersed phase while oil is the continuous phase, thus forming a W/O emulsion. When a pigment is combined with a lipophobic emulsifier (that is, hydrophilic), oil is the dispersed phase and water is the continuous phase, thus forming an O/W emulsion.
When present in an emulsion, pigments are commonly or typically included in the outer phase. In the case of water-in-oil emulsions, the pigments are typically located in the oil phase. Accordingly, a challenge facing the personal care industry is to provide an efficient formulation that would maintain pigments and especially untreated pigments in the water phase of a water-in-oil emulsion.